import java.util.Arrays;

class Dog {
    public String name;
    public int age;
    public String color;
    public void back() {
        System.out.println("wwww");
    }
    public void ser() {
        System.out.println("aaaaa");
    }


}
class value1 {
    public int val;
}
class value2 {
    public int val;
    public String name;
}
public class Test {
    public static void main(String[] args) {

      /*  int a = 10;
        int b = 30;
        int[] arr = {1,2,3};
*/
        int[] arr = null;
        System.out.println(arr[0]);

      /*  int[] array = {10, 20, 30, 40, 50};
        String ret = Arrays.toString(array);
        System.out.println(ret);*/


       /* for (int x : array) {
            System.out.println(x);
        }*/


      /*  for (int i = 0 ; i < array.length; i++) {
            System.out.println(i);
        }*/



        /*int[]array = new int[]{10, 20, 30, 40, 50};
        System.out.println(array[0]);
        System.out.println(array[1]);
        System.out.println(array[2]);
        System.out.println(array[3]);
        System.out.println(array[4]);*/

/*
        int[] array = {1, 2, 3};

        System.out.println(array[3]); // 数组中只有3个元素，下标一次为：0 1 2，array[3]下标越界
*/


      /*  int[]array = new int[]{10, 20, 30, 40, 50};
        System.out.println(array[0]);
        System.out.println(array[1]);
        System.out.println(array[2]);
        System.out.println(array[3]);
        System.out.println(array[4]);
        // 也可以通过[]对数组中的元素进行修改
        array[0] = 100;
        System.out.println(array[0]);
*/

    }
}